Modern disc drives are commonly used in a multitude of computer environments, ranging from super computers to notebook computers, to store large amounts of data in a form that is readily available to a user. Typically, a disc drive has one or more magnetic discs that are rotated by a spindle motor at a constant high speed. Each disc has a data storage surface divided into a series of generally concentric data tracks that are radially spaced across a band having an inner diameter and an outer diameter. The data is stored within the data tracks on the disc surfaces in the form of magnetic flux transitions. The flux transitions are induced by an array of read/write heads. Typically, each data track is divided into a number of data sectors where data is stored in fixed size data blocks.
The read/write head includes an interactive element such as a magnetic transducer. The interactive element senses the magnetic transitions on a selected data track to read the data stored on the track. Alternatively, the interactive element transmits an electrical signal that induces magnetic transitions on the selected data track to write data to the track.
Each of the read/write heads is mounted to a rotary actuator arm and is selectively positioned by the actuator arm over a pre-selected data track of the disc to either read data from or write data to the data track. The read/write head includes a slider assembly having an air bearing surface that, in response to air currents caused by rotation of the disc, causes the head to fly adjacent to the disc surface with a desired gap separating the read/write head and the corresponding disc.
Typically, multiple center-open discs and spacer rings are alternately stacked on a spindle motor hub. The hub, defining the core of the stack, serves to align the discs and spacer rings around a common axis. Collectively the discs, spacer rings and spindle motor hub define a disc pack assembly. The surfaces of the stacked discs are accessed by the read/write heads which are mounted on a complementary stack of actuator arms which form a part of an actuator assembly. The actuator assembly generally includes head wires which conduct electrical signals from the read/write heads to a flex circuit which, in turn, conducts the electrical signals to a flex circuit connector mounted to a disc drive base deck.
When the disc drive is not in use, the read/write heads are parked in a position separate from the data storage surfaces of the discs. Typically, a landing zone is provided on each of the disc surfaces where the read/write heads are positioned before the rotational velocity of the spinning discs decreases below a threshold velocity which sustains the air bearing. The landing zones are generally located near the inner diameter of the discs.
Generally, the actuator assembly has an actuator body that pivots about a pivot mechanism disposed in a medial portion thereof. A motor, such as a voice coil motor, selectively positions a proximal end of the actuator body. This positioning of the proximal end in cooperation with the pivot mechanism causes a distal end of the actuator body, which supports the read/write heads, to move radially across the face of the discs. The function of the pivot mechanism is crucial in meeting performance requirements associated with the positioning of the actuator assembly. A typical pivot mechanism has two ball bearings with a stationary shaft attached to an inner race and a sleeve attached to an outer race. The sleeve is also attached to a bore in the actuator body. The stationary shaft typically is attached to the base deck and the top cover of the disc drive.
A well known problem occurs as the result of thermal cycling which alters the compressive force that retains the sleeve in the actuator body. This is especially true when many or all the components of the cartridge bearing are made of steel in order to increase the strength and wear resistance. The actuator body is typically made of aluminum or magnesium to minimize the weight and inertia. The different materials provides a differential thermal expansion, that is, the actuator and cartridge bearing expand and contract at different rates and to different extents in a given temperature range.
A solution to the differential thermal expansion problem is to provide a resilient mounting of the actuator body to the cartridge bearing, so that relative thermal expansion and contraction can occur without affecting the preload or stress on the cartridge bearing. Such a solution involves providing an eccentric bore in the actuator body so that the cartridge bearing contacts the actuator body along a minimum contact surface, the rest of the cartridge bearing thus unencumbered and free to expand and contract during thermal cycling. The primary drawback to such a solution is that by minimizing the support of the actuator body makes the actuator assembly susceptible to undesired deflection which results in positional overshooting during data seek routines due to the torsion on the actuator body.
There is a long felt need in the industry for an improved apparatus for attaching the actuator body to the cartridge bearing, the improved apparatus combining the performance benefits of the rigid attachment, which minimizes overshoot conditions, with the performance benefits of the resilient attachment, which allows for differential thermal expansion of mating components.